Hot-Work Die Steel Electroslag Remelted Ingot and Manufacturing Method Thereof

ABSTRACT

The present invention discloses to a Hot-work die steel electroslag remelted ingot and a manufacture method thereof. The electroslag remelted ingot comprises the following chemical components, C: 0.36-0.41%, Si: 0.80-1.10%, Mn: 1.00-3.00%, Cr: 4.90-5.40%, Mo: 1.35-1.55%, V: 0.4-0.7%, Ni≤0.04%, Cu≤0.04%%, S≤0.003%, P≤0.012%, O≤0.0015%, H≤0.0002%, N≤0.006%, 0.05%≤RE≤0.20%, the balance being Fe. The above percentage is percentage by mass. According to the present invention, the features of electroslag remelting under inert gas protection are fully combined and a rare earth alloy is precisely fed during the electroslag remelting, thus exerting the excellent effects of RE inclusion modification and micro-alloying under high purity and high uniformity conditions and realizing high-quality and high-performance Hot-work die steel.

TECHNICAL FIELD

The present invention relates to the field of special steel smelting and processing, and more particularly to a high quality hot-work die steel electroslag remelted ingot and a manufacturing method thereof.

BACKGROUND ART

The hot-work die steel has high strength, heat resistance, wear resistance, and good thermal fatigue performance at high temperature, and at present, is a special steel widely applied to the dies such as a forging die, a hot extrusion die, a die-casting die and the like. The annual output of die steel in China is about 2.4 million tons, and there is a need of import about 100,000 tons of high-quality die steel, which will cost about 6 billion Chinese RMB. The imported die steel almost takes up the entire high-end market of die steel, with a price 3-5 times higher than that of domestic similar products. The main reason is that foreign die steel adopts the strict parameter control including steel purity, heat treatment structure refinement, and impact toughness. At present, compared with the international advanced technology such as in Sweden, Germany, the United States, Japan, and France, the domestic alloy die steel still has a certain gap in terms of variety, quality, size specification and performance, and it is still difficult to meet the market demand.

Steel purity is one of the key technologies in the research and development of high-performance die steel. With the improvement of new generation steel smelting technology, the content of O (Oxygen), S (Sulfur), and H (Hydrogen) in the steel ingot is greatly reduced, in which O≤0.001% and H≤0.0003%, which forms a foundation for the development of high-quality die steel. In order to further reduce the content of impurities, the steel electroslag remelting refining furnaces are indispensable equipment in addition to conventional refining equipment. By choosing a reasonable slag system, optimizing and adjusting the electroslag melting rate, and carrying out high-temperature homogenization treatment after slow cooling in the slag ingot, the segregation degree of carbides can be improved sufficiently, the number of eutectic carbides can be reduced, the particles can be smaller, and the composition can be more uniform.

In recent years, rare earth (RE) elements dominated by Y (Yttrium), La (Lanthanum), and Ce (Cerium) have been widely used in steels, especially in special steels and structural steels, largely because that these rare earth elements are chemically active, and easily react with O and S in the molten steel to form stable RE compounds, such as RE₂O₃, RE₂S₃, and REOS. The segregation of rare earth elements at grain boundaries will also play a role in cleaning the grain boundaries. The segregation of impurity elements, such as O and S, at grain boundaries will be reduced by rare earth elements. The risk of banded segregation leading to cracking is also reduced. The trace solid solution of rare earth atoms can also cause lattice distortion, dislocation proliferation, and additional stress field, a large amount of twin crystals can be formed for adjusting strain energy, and the comprehensive performance can be greatly improved due to the increase of twin crystals and dislocation. Therefore, the rare earth elements have the functions of deep deoxidation, desulfurization, hydrogen evolution and preferential carbide precipitation.

However, there are still some technical problems in the application of rare earth elements in the steel. At present, the traditional industrial addition methods, such as adding in a refining furnace, adding in a crystallizer, adding in a vacuum furnace, etc. tend to cause the unstable content of rare earth in the molten steel, and unavailable continuous casting due to the blockage of a casting nozzle, etc.

Therefore, in view of the defects of the prior art, a new technique needs to be designed.

SUMMARY OF THE INVENTION

The object of the present invention is to obtain a high-purity, high-uniformity hot-work die steel electroslag remelted ingot by feeding a rare earth alloy wire in the electroslag remelting stage and improving the process and slag system.

To achieve the foregoing objects, the present invention provides a hot-work die steel electroslag remelted ingot comprising the following chemical components, C: 0.36-0.41%, Si: 0.80-1.10%, Mn: 1.00-3.00%, Cr: 4.90-5.40%, Mo: 1.35-1.55%, V: 0.4-0.7%, Ni≤0.04%, Cu≤0.04%%, S≤0.003%, P≤0.012%, O≤0.0015%, H≤0.0002%, N≤0.006%, 0.05%≤RE≤0.20%, the balance being Fe, and the above percentages being percentages by mass.

As a further improvement of the present invention, the RE is a binary compound of Y and La, or a binary compound of Y and Ce, or a ternary compound of Y, La, and Ce.

As a further improvement of the present invention, the mass percentage of Y in the Hot-work die steel electroslag remelted ingot is 0.02%≤Y≤0.15%.

As a further improvement of the present invention, the mass percentage of La or Ce when present in the Hot-work die steel electroslag remelted ingot is 0.015%≤La≤0.02%, 0.015%≤Ce≤0.03%.

The present invention also provides a method of manufacturing the hot-work die steel electroslag remelted ingot which includes the following steps: (1) smelting, (2) secondary refining, (3) vacuum degassing, (4) die casting, and (5) atmospheric protection electroslag remelting.

As a further improvement of the present invention, the smelting can be performed with a converter or an electric furnace. the secondary refining is performed under protection of soft-blowing argon, with a time for soft blowing controlled to be 8-10 min, vacuum degassing is performed for greater than 20 min. The die casting is performed to obtain an electrode ingot which has a mass percentage of O, H, and N satisfying the following conditions: O≤0.001%, H≤0.0002%, N≤0.005%.

As a further improvement of the present invention, in step (5), an atmosphere protection constant melting rate electroslag remelting process is used, an inert gas of 2-10 ba is used for electroslag remelting under pressure protection, with an oxygen content in the protective cover of less than 50 ppm, and a melting rate of the electrode ingot designed to be 500 kg/h.

As a further improvement of the present invention, in step (5), a rare earth alloy is further fed through the crystallizer feed port, the rare earth alloy is a particulate RE-Fe alloy. RE accounts for 60-70% of the whole mass, Fe accounts for 30-40%, RE is one or more of La, Ce, and Y, the particle size of the rare earth alloy is 0.5-1.5 mm, and the feeding rate is 7-10 g/min.

As a further improvement of the present invention, a pre-molten slag is added during the electroslag remelting in the step (5). Each component in the pre-molten slag has a mass percentage of 70% CaF₂, 15% Al₂O₃, 10% RE₂O₃ and 5% MgO, and RE is one or more of La, Ce, and Y.

As a further improvement of the present invention, the pre-molten slag is proportioned according to a ratio of the slag system, and then placed in an environment of 600-750° C. for continuous firing for more than 8 h.

As a further improvement of the present invention, the pre-slag after firing has a content of crystal water of 0.006-0.05%.

As a further improvement of the present invention, after the hot-work die steel electroslag remelted ingot is subjected to forging annealing, the segregation is controlled within the AS4 grade, and the banded structure is controlled within the SA1 grade.

The advantages of the present invention are as follows: due to the fact that the inert gas can protect the electroslag remelting, accurate feeding of a rare earth alloy wire in an electroslag remelting refining furnace is realized. The excellent effects of RE inclusion modification and micro-alloying under high-purity and high-uniformity conditions are achieved.

The specific beneficial effects are shown as follows:

1. As rare earth elements may diffuse through vacancy mechanism to occupy the defect locations such as lattice nodes of iron or vacancy of the matrix, a pinning role of rare earth on solid solution carbon is exhibited and carbon diffusion is inhibited. The rare earths tend to segregate at the grain boundaries, so the morphology and distribution of primary carbides can be improved, which is beneficial to the improvement of comprehensive properties of die steel.

2. On the premise of obtaining high clean steel by electroslag process under atmosphere protection, the deep deoxidation and desulfurization effects of rare earth elements can be further exerted, and sub-micron rare earth composite inclusions can be formed, which can improve the impact toughness and thermal stability of matrix.

3. Feeding rare-earth alloy in the electroslag remelting refining furnace can fully play the role of micro-alloying of rare-earth elements in high-clean molten steel, due to the defect occupation of grain boundary and the influence of alloying elements (Cr, V, Mo), the banded segregation can be sufficiently reduced, the structure uniformity can be improved, and the metallurgical quality of electroslag ingot will be improved.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described in detail below with reference to the specific embodiments shown in the accompanying drawings.

In order to make the specific implementation mode more convincing, the design principle of each chemical component in the electroslag remelted ingot of the present invention will be described specifically.

C: Carbon can be partially dissolved into the matrix in the steel for solid solution strengthening. Part of the carbon forms alloy carbides with the alloying elements. The hardening capacity and hardenability of the steel can be improved by increasing the content of carbon properly. However, excessive high carbon content will form excessive carbides and tissue segregation, affecting the impact toughness of the steel. However, excessive low content of carbon element will result in less alloy carbide formed by the combination of carbon and other alloying elements, thus affecting the hardness, wear resistance, and high temperature performance of the steel. In carbon steel, the thermal conductivity decreases as the carbon increases, but in alloy steel, the effect of carbon and alloying elements should be considered to ensure the thermal conductivity and wear resistance. Therefore, the carbon content is controlled at 0.36-0.41%.

Si: Silicon element has a solid solution strengthening effect. By lowering the silicon content, the macrostructure will be more uniform and the undercooling of the components at the solidification interface during solidification will be reduced, resulting in increased plasticity and toughness. The silicon element may slow down and may effectively hinder the decomposition of martensite in the steel during tempering. Excessive high silicon content will aggravate the decarburization sensitivity of the steel, and increase the overaging rate of carbide aggregation, resulting uncontrollability. Silicon has a negative effect on the thermal conductivity in the steel, which will be greatly reduced as the content of silicon increases. Therefore, the content of silicon in this experimental material should be controlled at 0.80-1.10%.

Mn: As a weak carbide forming element, manganese has a solid solution strengthening effect to improve the strength and hardness of ferrite and austenite. Manganese element can increase and stabilize the content of retained austenite in the steel, by appropriately increasing the content of Mn herein, the amount of retained austenite during quenching will be increased, thereby contributing to improving the impact toughness and thermal fatigue resistance of the steel. However, excessive high content of manganese will promote the segregation of harmful elements to increase the brittleness, weaken the corrosion resistance of the steel, and reduce the thermal conductivity and welding performance, etc. By adding mixed rare earth elements herein, the segregation problem caused by the higher Mn content can be reduced, so that the Mn content in the new die steel is maintained at a higher level. The Mn content is designed to be 1.00-3.00%.

Cr: There is a solid solution of chromium element in ferrite to form carbides. Chromium element is added in most Hot-work die steel to precipitate Cr7C3 and Cr23C6 carbides in the steel during tempering. These carbides can not only improve the tempering softening resistance of the steel, but also produce red hardness and improve the hot strength of the steel. However, when the tempering temperature is higher than 600° C., chromium carbides are rapidly aggregated and coarsened, resulting a poor tempering resistance of the steel. Therefore, the content of Cr is designed to be 4.90-5.40%.

Mo: Molybdenum can improve hardenability and hot strength of the steel, decrease tempering brittleness, increase tempering stability, refine grain, and improve red hardness. The stability of steel austenite and hardenability of the steel are improved by adding Mo element. As a carbides forming element, Mo combines with carbon element to form stable M2C alloy carbide precipitation in the tempering process of the steel, which has a better secondary hardening effect. Since molybdenum precipitates in the form of M2C in parallel fine needle-like sites on the subgrain boundaries within the martensite lath during tempering, it remains coherent with the matrix, thus increasing high-temperature hardness of the steel. By increasing the content of molybdenum in the steel, fine carbides can be formed while increasing the recovery and recrystallization temperature of the tempered martensite, and the hot strength and thermal stability of the die steel can be further improved. The increase in molybdenum content in the steel allows to obtain more M2C alloy carbides during tempering and generate a greater secondary strengthening effect, which plays an important role in improving the hardness and wear resistance of the steel. In addition, molybdenum is an element for improving the thermal conductivity of the steel, so molybdenum is considered as the main alloying element in this experimental material, which has a content of 1.35-1.55% as one of the important alloying elements in this design.

V: As a strong carbide forming element, vanadium can improve the wear resistance in the steel, and can also hinder the growth of grain, thus refining the grain. Vanadium carbide has a high solid solubility product in austenite, and a small tendency of solidification structure cracking caused by precipitation at high temperature. The addition of proper amount of vanadium in the steel is beneficial to austenite recrystallization, so recrystallization control is easy to be carried out, and uniform grain can be obtained in a wide temperature range. The addition of vanadium in martensitic steel can increase the tempering softening resistance of the steel, so that the steel can maintain the martensite lath morphology or precipitates vanadium carbide during tempering, resulting in secondary hardening effect. In this patent, since a certain amount of mixed rare earth elements is added, a certain effect is exerted on refining the grains of prior austenite, therefore, the content of V is reduced. Therefore, the content of V is designed to be 0.4-0.7%.

The remaining Ni, Cu, S, P are unavoidable impurity components in the steel.

The function of the rare earth elements (abbreviated as RE) in the present invention mainly includes the following aspects:

1) compared with light rare earths, the rare earth composite inclusions formed by heavy rare earth Y with O and S are lighter in density and more likely to float up and enter the slag system, so the ability to purify molten steel is greatly improved, and it is easy to improve the balance of the slag system, therefore, Y is the main additive element in RE in this patent; the combination ability of Ce and La with O and S is stronger than that of Y, and it is easier to form fine and dispersed inclusions, which is beneficial to reduce the size of original non-metallic inclusions and improve the morphology of inclusions;

2) the addition of mischmetal in the electroslag remelting process can give full play to the micro-alloying effect of RE, for example, RE is easy to occupy in the grain boundary, thereby reducing the segregation of harmful elements, especially Cr phase, at the grain boundary. In addition, RE can also improve the distribution morphology of carbide in crystal boundary, break continuous fibrous distribution easily, and form spherical distribution more easily, thereby improving the strength and toughness;

3) in view of the microstructure, the addition of Y, La, and Ce can also reduce the stacking fault energy and increase the twin ratio, thus playing the role of twinning-induced plasticity (TWIP). It is also possible to refine the size of the martensite blocks or laths to optimize the overall properties of the Hot-work die steel.

The present invention is further described below with reference to the following examples.

EXAMPLE 1

The purchased raw materials are smelted with a converter or an electric furnace, and then is subjected to secondary refining under protection of soft-blowing argon, with a time for soft blowing controlled to be 8 min. Then a vacuum degassing for 22 min is performed, and the die casting is performed to obtain an electrode ingot which has a mass percentage of O, H, and N satisfying the following conditions after detection: O≤0.001%, H≤0.0002%, N≤0.005%;

Then the electrode ingot is subjected to electroslag remelting under atmosphere protection, specifically a constant melting rate electroslag remelting process under atmosphere protection is used. An inert gas 2 ba is used for electroslag remelting under pressure protection, with an oxygen content in the protective cover of less than 50 ppm, and a melting rate of the electrode ingot designed to be 500 kg/h, and said electroslag remelted ingot is obtained after electroslag remelting.

In the process of electroslag remelting, a granular RE-Fe rare earth alloy is also simultaneously fed through a crystallizer feed port. RE accounts for 60% of the whole mass, Fe accounts for 40%, and RE is a combination of La, Ce, and Y, the alloy had a particle size of 0.5 mm and a feeding rate of 7 g/min.

In addition, in the process of electroslag remelting, it is also necessary to add a premelted slag. Each component in the pre-molten slag has a mass percentage of 70% CaF₂, 15% Al₂O₃, 10% RE₂O₃ and 5% MgO, and RE is one or more of La, Ce, and Y; the pre-molten slag is proportioned according to a ratio of the slag system, and then placed in an environment of 600° C. for continuous firing for 9 h; and the pre-slag after firing had a content of crystal water of 0.05%.

The mass percentage of each component in the electroslag remelted ingot produced through the above-mentioned steps is as follows: C: 0.36%, Si: 1.10%, Mn: 1.00%, Cr: 5.40%, Mo: 1.35%, V: 0.7%, Ni: 0.04%, Cu: 0.04%%, S: 0.003%, P: 0.012%, O: 0.0015%, H: 0.0002%, N: 0.006%, Y: 0.02%, La: 0.015%, Ce: 0.015%, and the balance being Fe.

EXAMPLE 2

The purchased raw materials are smelted with a converter or an electric furnace, and then subjected to secondary refining under protection of soft-blowing argon, with a time for soft blowing controlled to be 10 min. Then a vacuum degassing is performed for more than 25 min, and the die casting is performed conventionally to obtain an electrode ingot which has a mass percentage of O, H, and N satisfying the following conditions after detection: O≤0.001%, H≤0.0002%, N≤0.005%.

Then the electrode ingot is subjected to electroslag remelting under atmosphere protection, specifically a constant melting rate electroslag remelting process under atmosphere protection is used. An inert gas 10 ba is applied for electroslag remelting under pressure protection, with an oxygen content in the protective cover of less than 50 ppm, and a melting rate of the electrode ingot designed to be 500 kg/h, and said electroslag remelted ingot is obtained after electroslag remelting.

In the process of electroslag remelting, a granular RE-Fe rare earth alloy is also simultaneously fed through a crystallizer feed port. RE accounts for 70% of the whole mass, Fe accounts for 30%, and RE is a combination of La, Ce, and Y, the alloy had a particle size of 1.5 mm and a feeding rate of 10 g/min.

In addition, in the process of electroslag remelting, it is also necessary to add a premelted slag. Each component in the pre-molten slag has a mass percentage of 70% CaF₂, 15% Al₂O₃, 10% RE₂O₃ and 5% MgO, and RE is a combination of Ce and Y. The pre-molten slag is proportioned according to a ratio of the slag system, and then placed in an environment of 750° C. for continuous firing for more than 8 h; and the pre-slag after firing has a content of crystal water of 0.006%.

The mass percentage of each component in the electroslag remelted ingot produced through the above-mentioned steps is as follows: C: 0.41%, Si: 0.80%, Mn: 3.00%, Cr: 4.90%, Mo: 1.55%, V: 0.4%, Ni: 0.03%, Cu: 0.01%, S: 0.002%, P: 0.012%, O: 0.001%, H: 0.00015%, N: 0.0045%, Y: 0.15%, Ce: 0.03%, and the balance (remaining substance) is Fe.

EXAMPLE 3

The purchased raw materials are smelted with a converter or an electric furnace, and then subjected to secondary refining under protection of soft-blowing argon, with a time for soft blowing controlled to be 9 min, then subjected to vacuum degassing for more than 21 min. The die casting is performed to obtain an electrode ingot which has a mass percentage of O, H, and N satisfying the following conditions after detection: O≤0.001%, H≤0.0002%, N≤0.005%;

Then the electrode ingot is subjected to electroslag remelting under atmosphere protection, specifically a constant melting rate electroslag remelting process under atmosphere protection is used, an inert gas 8 ba is used for electroslag remelting under pressure protection, with an oxygen content in the protective cover of less than 50 ppm, and a melting rate of the electrode ingot is designed to be 500 kg/h. The electroslag remelted ingot is obtained after electroslag remelting.

In the process of electroslag remelting, a granular RE-Fe rare earth alloy is also simultaneously fed through a crystallizer feed port, wherein RE accounts for 65% of the whole mass, Fe accounts for 35%, and RE is a combination of La and Y, the alloy has a particle size of 1 mm and a feeding rate of 8 g/min.

In addition, in the process of electroslag remelting, it is also necessary to add a premelted slag, wherein each component in the pre-molten slag had a mass percentage of 70% CaF₂, 15% Al₂O₃, 10% RE₂O₃ and 5% MgO, and RE is a combination of La and Y. The pre-molten slag is proportioned according to a ratio of the slag system, and then placed in an environment of 700° C. for continuous firing for 10 hours The pre-slag after firing has a content of crystal water of 0.02%.

The mass percentage of each component in the electroslag remelted ingot produced through the above-mentioned steps is as follows: C: 0.39%, Si: 0.90%, Mn: 2.00%, Cr: 5.10%, Mo: 1.45%, V: 0.55%, Ni: 0.022%, Cu: 0.03%, S: 0.0015%, P: 0.008%, O: 0.0009%, H: 0.0001%, N: 0.004%, Y: 0.10%, La: 0.02%, and the remaining substance is Fe.

EXAMPLE 4

The purchased raw materials are smelted with a converter or an electric furnace, and then subjected to secondary refining under protection of soft-blowing argon, with a time for soft blowing controlled to be 8 min, then subjected to vacuum degassing for more than 24 min. The die casting is performed to obtain an electrode ingot which has a mass percentage of O, H, and N satisfying the following conditions after detection: O≤0.001%, H≤0.0002%, N≤0.005%.

Then the electrode ingot is subjected to electroslag remelting under atmosphere protection, specifically a constant melting rate electroslag remelting process under atmosphere protection is used. An inert gas 3 ba is applied for electroslag remelting under pressure protection, with an oxygen content in the protective cover of less than 50 ppm. A melting rate of the electrode ingot is designed to be 500 kg/h. The electroslag remelted ingot is obtained after electroslag remelting.

In the process of electroslag remelting, a granular RE-Fe rare earth alloy is also simultaneously fed through a crystallizer feed port. RE accounts for 68% of the whole mass, Fe accounts for 32%, and RE is a combination of La, Ce, and Y, the alloy had a particle size of 1.2 mm and a feeding rate of 9 g/min.

In addition, in the process of electroslag remelting, it is also necessary to add a premelted slag, wherein each component in the pre-molten slag had a mass percentage of 70% CaF₂, 15% Al₂O₃, 10% RE₂O₃ and 5% MgO, and RE is a combination of La, Ce, and Y; the pre-molten slag is proportioned according to a ratio of the slag system, and then placed in an environment of 680° C. for continuous firing for 11 h; and the pre-slag after firing had a content of crystal water of 0.03%.

The mass percentage of each component in the electroslag remelted ingot produced through the above-mentioned steps is as follows: C: 0.36%, Si: 1.0%, Mn: 1.80%, Cr: 4.95%, Mo: 1.38%, V: 0.49%, Ni: 0.02%, Cu:0.03%, S: 0.003%, P: 0.012%, O: 0.0015%, H:0.0002%, N: 0.006%, Y: 0.15%, La: 0.02%, Ce: 0.03%, and the balance being Fe.

EXAMPLE 5

The purchased raw materials are smelted with a converter or an electric furnace, and then subjected to secondary refining under protection of soft-blowing argon, with a time for soft blowing controlled to be 9 min, then subjected to vacuum degassing for more than 24 min. The die casting is performed to obtain an electrode ingot which has a mass percentage of O, H, and N satisfying the following conditions after detection: O≤0.001%, H≤0.0002%, N≤0.005%.

Then the electrode ingot is subjected to electroslag remelting under atmosphere protection, specifically a constant melting rate electroslag remelting process under atmosphere protection is used. An inert gas 6 ba is applied for electroslag remelting under pressure protection, with an oxygen content in the protective cover of less than 50 ppm, and a melting rate of the electrode ingot designed to be 500 kg/h. The electroslag remelted ingot is obtained after electroslag remelting.

In the process of electroslag remelting, a granular RE-Fe rare earth alloy is also simultaneously fed through a crystallizer feed port. RE accounts for 70% of the whole mass, Fe accounts for 30%, and RE is a combination of Ce and Y. The alloy has a particle size of 1.2 mm and a feeding rate of 9 g/min.

In addition, in the process of electroslag remelting, it is also necessary to add a premelted slag, wherein each component in the pre-molten slag had a mass percentage of 70% CaF₂, 15% Al₂O₃, 10% RE₂O₃ and 5% MgO, and RE is combination of Ce and Y. The pre-molten slag is proportioned according to a ratio of the slag system, and then is placed in an environment of 750° C. for continuous firing for more than 9 hours; and the pre-slag after firing has a content of crystal water of 0.009%.

The mass percentage of each component in the electroslag remelted ingot produced through the above-mentioned steps is as follows: C: 0.40%, Si: 0.85%, Mn: 2.00%, Cr: 5.10%, Mo: 1.50%, V: 0.5%, Ni: 0.022%, Cu: 0.031%, S: 0.002%, P: 0.010%, O: 0.001%, H: 0.00018%, N: 0.003%, Y: 0.12%, Ce: 0.02%, and the remaining substance is Fe.

EXAMPLE 6

The purchased raw materials are smelted with a converter or an electric furnace, and then subjected to secondary refining under protection of soft-blowing argon, with a time for soft blowing controlled to be 10 min, then subjected to vacuum degassing for more than 23 min. The die casting is performed to obtain an electrode ingot which has a mass percentage of O, H, and N satisfying the following conditions after detection: O≤0.001%, H≤0.0002%, N≤0.005%;

Then the electrode ingot is subjected to electroslag remelting under atmosphere protection, specifically a constant melting rate electroslag remelting process under atmosphere protection is used, an inert gas 5 ba is used for electroslag remelting under pressure protection, with an oxygen content in the protective cover of less than 50 ppm, and a melting rate of the electrode ingot designed to be 500 kg/h, and said electroslag remelted ingot is obtained after electroslag remelting.

In the process of electroslag remelting, a granular RE-Fe rare earth alloy is also simultaneously fed through a crystallizer feed port, wherein RE accounts for 62% of the whole mass, Fe accounts for 38%, and RE is a combination of La and Y. The alloy has a particle size of 0.8 mm and a feeding rate of 9 g/min.

In addition, in the process of electroslag remelting, it is also necessary to add a premelted slag. Each component in the pre-molten slag has a mass percentage of 70% CaF₂, 15% Al₂O₃, 10% RE₂O₃ and 5% MgO, and RE is a combination of La and Y. The pre-molten slag is proportioned according to a ratio of the slag system, and then placed in an environment of 720° C. for continuous firing for 9 h; and the pre-slag after firing has a content of crystal water of 0.01%.

The mass percentage of each component in the electroslag remelted ingot produced through the above-mentioned steps is as follows: C: 0.39%, Si: 0.98%, Mn: 2.20%, Cr: 5.20%, Mo: 1.42%, V: 0.65%, Ni: 0.020%, Cu: 0.02%, S: 0.0010%, P: 0.009%, O: 0.0008%, H: 0.0001%, N: 0.005%, Y: 0.08%, La: 0.02%, and the remaining substance is Fe.

EXAMPLE 7

The purchased raw materials are smelted with a converter or an electric furnace, and then subjected to secondary refining under protection of soft-blowing argon, with a time for soft blowing controlled to be 8 min, then subjected to vacuum degassing for more than 22 min, and the die casting is performed to obtain an electrode ingot which has a mass percentage of O, H, and N satisfying the following conditions after detection: O≤0.001%, H≤0.0002%, N≤0.005%.

Then the electrode ingot is subjected to electroslag remelting under atmosphere protection, specifically a constant melting rate electroslag remelting process under atmosphere protection is used, an inert gas 5 ba is used for electroslag remelting under pressure protection, with an oxygen content in the protective cover of less than 50 ppm, and a melting rate of the electrode ingot is designed to be 500 kg/h, and said electroslag remelted ingot is obtained after electroslag remelting.

In the process of electroslag remelting, a granular RE-Fe rare earth alloy is also simultaneously fed through a crystallizer feed port. RE accounts for 70% of the whole mass, Fe accounts for 30%, and RE is a combination of La, Ce, and Y, the alloy had a particle size of 1.0 mm and a feeding rate of 7 g/min.

In addition, in the process of electroslag remelting, it is also necessary to add a premelted slag, wherein each component in the pre-molten slag had a mass percentage of 70% CaF₂, 15% Al₂O₃, 10% RE₂O₃ and 5% MgO, and RE is a combination of La, Ce, and Y. The pre-molten slag is proportioned according to a ratio of the slag system, and then placed in an environment of 690° C. for continuous firing for 10 h; and the pre-slag after firing had a content of crystal water of 0.03%.

The mass percentage of each component in the electroslag remelted ingot produced through the above-mentioned steps is as follows: C: 0.39%, Si: 0.99%, Mn: 1.20%, Cr: 5.12%, Mo: 1.40%, V: 0.56%, Ni: 0.02%, Cu:0.03%, S: 0.0017%, P: 0.0092%, O: 0.0007%, H:0.00011%, N: 0.003%, Y: 0.087%, La: 0.018%, Ce: 0.02%, and the remaining substance is Fe.

EXAMPLE 8

The purchased raw materials are smelted with a converter or an electric furnace, and then subjected to secondary refining under protection of soft-blowing argon, with a time for soft blowing controlled to be 10 min, then subjected to vacuum degassing for more than 23 min. The die casting is performed to obtain an electrode ingot which has a mass percentage of O, H, and N satisfying the following conditions after detection: O≤0.001%, H≤0.0002%, N≤0.005%;

Then the electrode ingot is subjected to electroslag remelting under atmosphere protection, specifically a constant melting rate electroslag remelting process under atmosphere protection is used, an inert gas 8 ba is used for electroslag remelting under pressure protection, with an oxygen content in the protective cover of less than 50 ppm, and a melting rate of the electrode ingot designed to be 500 kg/h. The electroslag remelted ingot is obtained after electroslag remelting.

In the process of electroslag remelting, a granular RE-Fe rare earth alloy is also simultaneously fed through a crystallizer feed port. RE accounts for 70% of the whole mass, Fe accounts for 30%, and RE is a combination of Ce and Y, the alloy has a particle size of 1.2 mm and a feeding rate of 7 g/min.

In addition, in the process of electroslag remelting, it is also necessary to add a premelted slag, wherein each component in the pre-molten slag had a mass percentage of 70% CaF₂, 15% Al₂O₃, 10% RE₂O₃ and 5% MgO, and RE is a combination of Ce and Y; the pre-molten slag is proportioned according to a ratio of the slag system, and then placed in an environment of 720° C. for continuous firing for 9 hours; and the pre-slag after firing had a content of crystal water of 0.03%.

The mass percentage of each component in the electroslag remelted ingot produced through the above-mentioned steps is as follows: C: 0.40%, Si: 0.89%, Mn: 2.20%, Cr: 5.00%, Mo: 1.52%, V: 0.52%, Ni: 0.024%, Cu: 0.024%, S: 0.002%, P: 0.009%, O: 0.001%, H: 0.00018%, N: 0.003%, Y: 0.065%, Ce: 0.02%, and the remaining substance is Fe.

COMPARATIVE EXAMPLE 1

This comparative example differs from Example 1 in that no rare earth element is added. Other elements and the manufacturing process are the same as in Example 1, and the remaining components are also Fe and inevitable impurity elements.

FIGS. 3 and 4 show the metallographic observation results of the banded structure characteristics and inclusion characteristic morphology of the electroslag remelted ingot subjected to high-temperature diffusion annealing.

COMPARATIVE EXAMPLE 2

This comparative example differs from Example 1 in that the rare earth elements are added in an amount of Y: 0.01%, La: 0.009%, Ce: 0.012%, with a total amount of RE of 0.031%. Other added elements and the manufacturing process are similar to Example 1, and the remaining is Fe and inevitable impurities.

COMPARATIVE EXAMPLE 3

This comparative example differs from Example 1 in that the rare earth elements are added in an amount of Y: 0.35%, La: 0.09%, Ce: 0.08%, with a total amount of RE of 0.52%, other added elements and the manufacturing process are similar to Example 1, and the remaining is Fe and some inevitable impurities.

COMPARATIVE EXAMPLE 4

This comparative example differs from Example 1 in that the rare earth elements are added in an amount of Y: 0.08%, La: 0.019%, Ce: 0.025%, with a total amount of RE of 0.124%. Other added elements and the manufacturing process are similar to Example 1, and the remaining is Fe and some inevitable impurities.

The preparation method differs from that of Example 1 in that rare earth alloy particles having a particle size of 5 mm are fed into the crystallizer feed port, with a feeding rate of 15 g/min.

Experimental tests are carried out on the electroslag remelted ingots prepared according to the above Examples and Comparative Examples, and the results are as follows:

The metallographic observation results of the banded structure and inclusions characteristic morphology of the electroslag remelted ingot prepared in Example 1 after being subjected to heat treatment are shown in FIGS. 1 and 2 . The metallographic observation results of the banded structure and the inclusion characteristic morphology of the electroslag remelted ingot prepared in Examples 2-8 after being subjected to heat treatment are almost consistent with those of FIGS. 1 and 2 . The metallographic observation results of the banded structure and the inclusion characteristic morphology of the electroslag remelted ingot prepared in Comparative Example 1 after being subjected to high-temperature diffusion annealing are shown in FIGS. 3 and 4 . FIGS. 1 and 3 are photos after ingot corrosion, FIGS. 2 and 4 are photos after ingot polishing.

It can be seen from FIGS. 1 and 2 that the addition of rare earth elements can obviously eliminate the banded structure characteristics. The comparison of the images in FIGS. 3 and 4 shows that the rare earth obviously modifies the inclusion, so that the size of the inclusion is refined, and the quantity of large-size inclusions is reduced.

The electroslag remelted ingot prepared by the above-mentioned Examples and Comparative Examples is subjected to a series of process steps of high-temperature diffusion annealing, ultra-refining treatment, forging, isothermal spheroidizing annealing, quenching and tempering to obtain a Hot-work die steel finished product, which is tested for the Rockwell hardness, longitudinal impact energy, and isotropy, and the results are shown in Table 1.

TABLE 1 Longitudinal Lateral impact impact Serial Particle Feeding energy energy Number Y/% Ce % La % RE/% size/mm rate g/min Hardness (Aku5) (Aku5) Isotropy Example 1 0.02  0.015 0.015 0.05 0.5 9 44 23.1 19.7 0.88 Example 2 0.15 0.03 — 0.18 1.5 10 45 23.3 19.8 0.88 Example 3 0.10 — 0.02  0.12 1.0 8 45 23.0 20.0 0.86 Example 4 0.15 0.03 0.02  0.20 1.2 9 43 22.8 19.9 0.88 Example 5 0.12 0.02 — 0.14 1.2 9 44 23.2 20.2 0.87 Example 6 0.08 — 0.02  0.10 0.8 9 44 22.9 20.1 0.87 Example 7 0.087 0.02 0.018 0.125 1.0 7 45 23.1 20.3 0.88 Example 8 0.065 0.02 — 0.085 1.2 7 44 22.7 19.6 0.86 Comparative — — — — — — 43 15.7 12.1 0.77 Example 1 Comparative 0.01  0.012 0.009 0.031 0.5 9 44 13.9 9.3 0.67 Example 2 Comparative 0.35 0.08 0.09  0.52 0.5 9 38 10.3 4.7 0.45 Example 3 Comparative 0.08  0.025 0.019 0.124 5 15 40 17.5 14.6 0.83 Example 4

As shown in Table 1, it is found from the properties of the electroslag remelted ingots prepared from the respective Examples and Comparative Examples after forging and heat treatment that, the impact toughness and isotropy of the Examples 1 to 8 added with RE are significantly better than those of the respective Comparative Examples, indicating that the addition of RE can optimize the properties of the Hot-work die steel, while the impact toughness and isotropy are significantly deteriorated with excessive RE content (Comparative Example 3). In addition, in Comparative Example 4, although the total amount of RE is controlled, the particle size of the rare earth alloy and the feeding rate far exceeded the requirements, so that the feeding rate and the melting rate of the electrode ingot did not match, resulting in a decrease in both impact energy and hardness, thus indicating that the particle size and the feeding rate of the rare earth alloy need to be strictly and precisely controlled to achieve the optimization of product properties.

In addition, it should be noted that the selection of the pre-slag to be added in the electroslag remelting process of the present invention is also optional, and the selection of the RE element in the pre-slag needs to be matched according to the rare earth element in the added rare earth particles, namely, which RE elements are used for feeding in the rare earth particles, and when the pre-slag is proportioned, it is necessary to match the oxides of the same RE element.

It should be understood that although this specification is described in accordance with the embodiments, not every embodiment includes only an independent technical solution. Such a description is merely for the sake of clarity, and those skilled in the art should take the specification as a whole. The technical solutions in the embodiments can also be appropriately combined to form other implementations which are comprehensible for those skilled in the art.

The foregoing detailed description is only specific illustration of possible embodiments of the present invention, rather than limiting the claimed scope of the present invention. All equivalent embodiments or changes made without departing from the technical spirit of the present invention should be included in the claimed scope of the present invention. 

What is claimed is:
 1. A hot-work die steel electroslag remelted ingot, comprising the following chemical components, C: 0.36-0.41%, Si: 0.80-1.10%, Mn: 1.00-3.00%, Cr: 4.90-5.40%, Mo: 1.35-1.55%, V: 0.4-0.7%, Ni≤0.04%, Cu≤0.04%% S≤0.003%, P≤0.012%, O≤0.0015%, H≤0.0002%, N≤0.006%, 0.05%≤RE≤0.20%, the remaining substance being Fe, and the above percentages being percentages by mass.
 2. The hot-work die steel electroslag remelted ingot according to claim 1, wherein the RE is a binary compound of Y and La, or a binary compound of Y and Ce, or a ternary compound of Y, La, and Ce.
 3. The hot-work die steel electroslag remelted ingot according to claim 2, wherein the mass percentage of Y in the hot-work die steel electroslag remelted ingot is 0.02%≤Y≤0.15%.
 4. The hot-work die steel electroslag remelted ingot according to claim 2, wherein the mass percentage of La or Ce when present in the hot-work die steel electroslag remelted ingot is 0.015%≤La≤0.02%, 0.015%≤Ce≤0.03%.
 5. A method for manufacturing the hot-work die steel electroslag remelted ingot according to claim 1, comprising the following steps: smelting, secondary refining, vacuum degassing, die casting, and atmosphere protection electroslag remelting.
 6. The method for manufacturing the hot-work die steel electroslag remelted ingot according to claim 5, wherein the smelting is performed by using a converter smelting or an electric furnace smelting; the secondary refining is performed under protection of soft-blowing argon, with a time for soft blowing controlled to be 8-10 minutes, the time for vacuum degassing needs to be greater than 20 minutes; and the die casting is performed to obtain an electrode ingot, wherein the mass percentages of O, H, and N in the electrode ingot satisfy the following conditions: O≤0.001%, H≤0.0002%, N≤0.005%.
 7. The method for manufacturing the hot-work die steel electroslag remelted ingot according to claim 5, characterized in that in the step of atmosphere protection electroslag remelting, an atmosphere protection constant melting rate electroslag remelting process is adopted, an inert gas of 2-10 ba is used for pressure protection electroslag remelting, the oxygen content in the protective cover is less than 50 ppm, and the melting rate of the electrode ingot is designed to be 500 kg/h.
 8. The method for manufacturing the hot-work die steel electroslag remelted ingot according to claim 5, wherein in the step of atmosphere protection electroslag remelting, a rare earth alloy is fed through a crystallizer feed port, the rare earth alloy being a particulate RE-Fe alloy, wherein RE accounts for 60-70% of the whole mass, Fe accounts for 30-40%, RE is one or more of La, Ce, and Y, the particle size of the rare earth alloy is 0.5-1.5 mm, and the feeding rate is 7-10 g/min.
 9. The method for manufacturing the hot-work die steel electroslag remelted ingot according to claim 5, wherein in the step of atmosphere protection electroslag remelting, a pre-molten slag is added, wherein each component in the pre-molten slag has a mass percentage of 70% CaF₂, 15% Al₂O₃, 10% RE₂O₃ and 5% MgO, and RE is one or more of La, Ce, and Y.
 10. The method for manufacturing the hot-work die steel electroslag remelted ingot according to claim 9, wherein the pre-molten slag is proportioned according to a ratio of the slag system, and then placed in an environment of 600-750° C. for continuous firing for more than 8 hours.
 11. The method for manufacturing the hot-work die steel electroslag remelted ingot according to claim 10, wherein a content of crystal water in the pre-molten slag after firing is 0.006-0.05%.
 12. The method for manufacturing the hot-work die steel electroslag remelted ingot according to claim 5, wherein the Hot-work die steel electroslag remelted ingot is subjected to forging annealing, and after forging annealing, a segregation is controlled within the AS4 grade, and a banded structure is controlled within the SA1 grade. 